EPR insights into aqueous solutions of gelatin and sodium dodecyl sulfate†

Abstract

The characteristics of the EPR spectra of the spin-probe 16-doxyl-stearic acid‡ methyl ester (16-DSE) solubilised in micelles of the anionic surfactant sodium dodecyl sulfate (SDS) have been examined as functions of SDS and gelatin concentrations. For simple SDS solutions, the rotational correlation time increases slightly with surfactant concentration whilst the polarity decreases slightly. In contrast, however, in the presence of gelatin these properties vary markedly as a function of the stoichiometric ratio of the concentration of surfactant to gelatin; the correlation time decreasing and the hyperfine coupling constant increasing with increasing surfactant concentration. In the presence of gelatin therefore, 16-DSE reports a very different micellar environment compared with the simple SDS case. Furthermore, this environment differs significantly from that observed in solutions of synthetic, non-ionic homopolymers and SDS. These features arise due to the varied characteristics of the amino acids present in the protein.